Electrophotographic reproduction material



Unite States 3,037,861 ELECTROPHOTOGRAPHIC REIRODUCTION MATERIAL This invention relates to photographic reproduction and more particularly to electrophotographic layers and electro-photographic processes, namely processes in which an electrostatic latent image is produced by utilizing the property of photoconduction (i.e. a variable conductivity dependent on the intensity of illumination).

The electrostatic latent image may be produced in a conventional exposure operation, for example by means of a lens-projected image or by contact-printing techniques, whereby a non-visible electrostatic charge pattern (the so-called electrostatic latent image) is created on a surface, in which pattern the charge density at any point is related to the intensity of illumination obtaining at that point during the exposure. The latent image may be developedi.e. rendered visible-by means of an electroscopic powder, such as a colored. synthetic resin powder, and the resulting visible image may be fixed by rendering the powder permanently adherent to a support on which the image is desired, for example in suitable cases by heating to soften or melt the powder particles and/or the surface of the image support, or by application of an electric field, or with volatile solvents.

In electro-photographic processes the electrostatic latent image is commonly formed on the surface of a photoconductive insulating layer carried on a support. For example, material comprising such support and photoconductive layer may be sensitized by applying a uniform surface charge to the free surface of the photoconductive layer, for example by means of a corona discharge, which charge is retained owing to the substantial insulating character, i.e. the low conductivity, of the layer in the dark. On exposure as described above, the photoconductive property of the layer causes the conductivity to increase in the illuminated areas to an extent dependent on the intensity of illumination, whereby the surface charge in the illuminated areas leaks away, leaving the charge located in the unilluminated areas, thus constituting the aforementioned charge pattern or electrostatic latent image. The electrostatic latent image can be developed (i.e. rendered visible) by means of an electroscopic powder which adheres to the charged areas, particularly if the powder carries a charge of opposite polarity to that of the charge on the photoconductive material. Such opposite charge may be obtained by using the powder in admixture with a carrier such that the powder becomes suitably charged triboelectrically. A suitable developer may consist of a toner, such as a pigmented resin, and a carrier such as glass beads, and the powder image produced may be rendered permanent (fixed) by for example softening such resin toner by heat so that it adatent heres to a support carying the powder imagewhich may be the original photoconductive material, or a separate support to which the powder image can have been transferred.

It has been usual hitherto, in producing photoconductive insulating layers on supports, to apply the photoconductive substance, for example as a solution or dispersion in an organic solvent, in admixture with a binding agent, with the object of increasing the insulating property of the layer and improving the homogeneity thereof, whereby the photoconductive substance should be present as extremely fine particles or preferably as a solid solution. The quality and uniformity of line, and even more of solid areas, in copies produced, is greatly affected by the nature of the binding agents used.

The present invention contemplates the provision and use of photoconductive insulating substances which may, if desired, be used Without admixture with binding agents to produce photoconductive insulating layers on supports, and may furthermore be used in the form of self-supporting foils as electrophotographic materials.

The invention provides a method of electrophotographic reproduction, which comprises the formation of an electrostatic latent image on a photoconductive insulating layer carried on a support, or on a self-supporting photoconductive insulating foil, said layer or foil consisting of or comprising a poly-N-carbazole as a photoconductive substance.

A preferred method of carrying out the invention comprises the steps of applying an electrostatic charge to a surface of a photoconductive insulating layer comprising a poly-N-vinyl-carbazole carried on a support, or of a photoconductive insulating foil comprising a poly- N-vinyl-carbazole, exposing the charged surface so as to produce thereon an electrostatic latent image corresponding to a master, developing the electrostatic latent image by means of an electroscopic powder, and fixing the powder image on the surface of the photoconductive layer or foil or on a separate image-carrier after transference of the powder image thereto.

The invention further provides a material for use in electrophotographic processes, being capable of being rendered light sensitive by applying an electrostatic charge thereto, and comprising a paper or other support carrying a photoconductive insulating layer comprising a poly-N-vinyl-carbazole.

While the layers are, in themselves, non-light-s ensitive, by applying a positive or negative electrostatic charge thereto, by means for example, of a corona discharge the layers are rendered light sensitive and can be used with long-wave UV. light of 3.600 to 4.200 A.U. in producing electrostatic latent images as described above. Very good images may be obtained by a short exposure under a master to a high-pressure mercury vapour lamp.

Although the layers when charged are but slightly sensitive to light in the visible spectrum, it has further been found that their spectral sensitivity can be extended into the visible part of the spectrum by the addition to the layers of sensitizers, preferably in the proportion 0.1 to 5 percent weight for weight of photoconductive substance. The most suitable sensitizers are dyestufi com- Reference (Schultz' Dyestufl Group Dyestufi Compound Farbstoiftabellen,

7th ed. Vol. 1 (1931) Brilliant Green No. 760 (p. 314). lyxictgriagluefifl go 8/2; Ep. ety 'ioe c o 8 p. 7 Triarylmethanfi dyes Crystal Violet No 785 (p. 329) Acid Violet 63 p u Ethyl Violet Rhodamine B Xanthene dyes:

866 (p. 366) Rmdammes Rhodamine G extra No 865 (p. 366) Sulphorhodamine B- No 863 (p, 364) True acid Eoslu G No 870 (p. 368) Eosin S No 883 (p. 375) gosh;1 A go. 331 Ep. ryt rosin o. 6 p. 7 Phthalems Phloxin No. 890 (p. 378) Rose Bengal N o 889 (p. 378). Fluorescein. N o. 880 (p. 373). Thiazine dyes, Methylene Blu N0. 1038 (p. 449).

, Acridine yellow N0. 901 (p. 883). Acrldlne dyes Aeridine orange" No. 908 (p. 387). V Trypaflavine No. 906 (P. 386). 7 Quiuoline dyes Pmacyaml g8: 35% EB: 33%: Quinone dyestuffs V No. 1141 (p. 499). Ketone dye-stuff Alizariu red 5.. c No. 1145 (p. 502). Quinizariu No. 1148 (p. 504). Cyanlne dyes Oyaninc- N0. 921 (p. 394). Chlorophyll Such sensitizers may be incorporated with like advantage in self-supporting foils of polyvinyl-carbazoles Y 7 Acids, for example:

Mineral acids, such the hydrogen halides, sulphuric acid and phosphoric acid; Organic carboxylic acids, such as acetic acid and the substitution products thereof, monochloro-acetic acid, di-

chloroacetic acid, trichloroacetic acid, phenylacetic acid, and 6-methyl-coumarinylacetic acid (4); maleic acid; cinnamic acid, benzoic acid, l-(4-diethylamino-benzoyl)-benzene-2-carboxy1ic acid, phthalic acid, and

tetrachlorophthalic acid, ,5-dibromo- 8-formyl-acrylic acid (muco-bromic acid), dibromo-maleic acid, 2- brorno-benzoic acid, gallic acid, 3-nitro-2-hydroxy-1- benzoic acid, Z-nitro-phenbxyacetic acid, 2-nitro-benzoic acid, 3-nitrobenzoic acid, 4-nitro benzoic acid, 3-

nitro-4-ethoxy-benzoic acid, 2-chl0ro-4-nitro-1-benzoic acid, 3-nitro-4-methoxy-benzoic acid, 4-nitro-l-methylbenzoic acid, Z-chloro-S-nitro-l-benzoic acid, 3-chlo-ro 6-nit-ro-1-benzoic acid, 4-chloro-3-nitro-l-benzoic acid, 5-chloro 3-nitro-2-hydroxy-benzoic acid, 4-chloro-2-hydroxy-benzoic acid, 2,4-dinitro-1-benzoic acid, Z-bromo- S-nitro-benzoic acid, 4-chlorophenyl-acetic acid, 2-chloro-cinnamic acid, 2-cyano-ci1mamic acid, 2,4-dich1orobenzoic acid, 3,5-dinitro-benzoic acid, 3,5-dinitr0-salicylic acid, malonic acid, mucic acid, acetosalicylic acid,

benzilic acid, butane-tetra-carboxylic acid, citric acid, 5 3

cyano-acetic acid, cyclohexane-dicarboxylic acid, cycloh exene-carboxylic acid, 9,10-dichl0ro-stearic acid, fumaric acid, itaconic acid, levulinic acid (levulic acid), malic acid, suocinic acid, u-bromo-propionic acid, abromo-stearic acid, citraconic acid, di-bromo-succinic acid, pyrene-2,3,7,8-tetra-carboxylicacid, tartaric acid; Organic sulphonic acids, such as 4-toluenesulph0nic' acid, and benzene sulphonic acid, 2,4-dinitro-1-methyl-ben zene--sulphonic acid, 2,6-dinitro-l-hydroxy-benzene- 4-sulphonic acid, Z-nitro-l-hydroxy-benzenei-sulphonic acid, 4-nitro-1-hydroxy-benzene-Z-sulphonic acid, 3-

, poly-vinyl-carbazole.

4 nitro-Z-methyl-l-hydroxy-benzene-S-sulfonic acid, 6- nitro l-methyl-l-hydroxybenzene-2-sulfonic acid, 4- chloro-1 hydroxy-benzene-3-sulf0nic acid, 2-chl0ro-3- :nitro 1 methyl-benzene-S-sulfonic acid, 2chloro-1- methyl-benzene-4-sulfonic acid;

Organic phosphonic acids, such as 4-chloro-3-nitro-benzene-phosphonic acid;

Nitrophenols, such as 4-nitrophenol, and picric acid;

Acid anhydrides, for example:

Acetic anhydn'de, succinic anhydride, maleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, and chrysene-Z,3,8,9-tetracarboxylic anhydride, di-bromomaleic acid anhydride;

Metal halides of the metals and metalloids of the groups IB, II through to group VIII of the periodical system, for example:

Aluminium chloride, zinc chloride, ferric chloride, tin tetrachloride (stannic chloride), arsenic trichloride, stannous chloride, antimony pentachloride, magnesium chloride, magnesium bromide,calcium bromide, calcium to dide, strontium bromide, chromic bromide, manganous chloride, ferrous chloride, cobaltous chloride, cobaltic chloride, cupric bromide, cuprous chloride, ceric chloride, cerous chloride, cerous bromide, mercuric chloride (corrosive sublimate), thorium chloride, arsenic triiodide;

Boron halide compounds, for example:

Boron trifluoride, and boron trichloride;

Organic substances containing CO-groups, which are substantially monomeric, for example:

Quinones, such as p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-dichloro benzoquinone, chloroanil, naphthoquinone-( 1,4) 2,3-dichloro-naphthoquinone-( 1,4), anthraquinone, Z-methyIanthraquinone, 1,4-dimet-hylanthraquinone, l-chloroanthraquinoue, anthraquinone- Z-carboxylic acid, 1,5-dichloroanthraquinone, 1-chloro- 4-nitroauthraquinone, phenanthrene-quinone, acenap-hthenequinone, pyranthrenequinone, chrysene-quinone, thio-naphthene-quinone, anthraquinone-l,8-disulfonic acid, and anthraquinone-2-aldehyde; t-riphthaloyl-benzene;

Aldehydes, such as bromal, 4-nitrobenzaldehyde, 2,'6-dichlorobenzaldehyde, 2-ethoxy-l-naphthaldehyde, anthIacene-9-aldehyde, pyrene3'-aldehyde, oxind0le-3- aldehyde, pyridine-2,6 -dialdehyde, biphenyl-4-aldehyde, furfural;

Ketones, such as acetophenone, benzophenone, 2-acetylnaphthalene, benzil, benzoin, S-benzoyl-acenaphthene, biacene-dione, Q-acetylanthracene, 9-benzoyl-anthracene, 4-(4'-dimethylamino-cinnamoyl)-1-acetylbenzene, acetoacetic acid-anilide, indandione-(LB), (1,3-diketohydrindene), acenaphthenequinone-dichloride, an-isil, 2,2-pyridil, fun'l.

The quantity of the substances required for obtaining the best possible improvement varies with the nature of such substance, but generally is from 0.01 to 5 percent, preferably from. 1 to 2 percent weight for Weight of the The addition of even a much smaller quantity causes a considerable increase of the sensitivity of the poly-vinyl-carbazole layer. Larger quantities of the additive substances even up to 20 percent weight for weight of the poly-vinyl carbazole, may be used if desired. "Non-volatile solid compounds amongst the class referred to are preferably used as the additive sub stances. Liquid or gaseous additive substances of the class referred to may also be used.

The invention further includes a material for use in electrophotographic processes comprising a self-supporting foil of poly-N-vinyl-carbazole which may contain a sensitizer being a dyestufi or other substance capable of modifying the spectral sensitivity of the foil when electrostatically charged, and/ or an additive of the class set forth above elfective to increase the photo-semiconductive capacity of the polyvinyl-carbazole and comprising acids, acid anhydrides, metal halides, boron halides, and organic carbonyl compounds.

Material embodying the invention, both in the form of a self-supporting foil and of a layer carried .on a support, may also be employed as record paper for charting purposes, for example for photographic recorders and like apparatus.

Polyvinyl-carbazoles, i.e. polymerisation products of N-vinyl-carbazole, are known in various stages of polymerisation. They have resin-like character, rendering superfluous the use of binding agents for the purpose of increasing the homogeneity of a photo-conductive insulating layer. High-molecular poly-N-vinyl carbazoles are available as commercial products, for example, the products marketed by the firm of Badische Anilinund Sodafabrik A.G., Ludwigshafen/Rhein, under the registered trademark Luvican, such as Luvican K 323, Luvican M 170 and Luvican K 260. They dissolve with strong fluorescence in many organic solvents. A method of producing said polyvinyl carbazole has been described in US. Patent 2,072,465, filed by W. Reppe et al. and assigned to I. G. Farbenindustrie Aktiengesellschaft. For the preparation of self-supporting, fibreless foils from the N-vinyl-carbazoles of high molecular weight known methods for the preparation of plastic foils may be used, such as casting from solutions of the polymers in organic solvents.

For application as a photoconductive insulating layer on a support, the polyvinyl carbazoles are preferably coated in organic solvents onto the support which may be of the kind commonly used in electro-photography, for example metal, paper or a plastic foil, in known manner for example by hopper coating or by direct coating. The polyvinyl carbazoles may be used for coating supports, also for aqueous dispersions or dispersions in organic solvents, with equally good results. Photoconductive insulating layers of exceptional uniformity are obtained by this means with which excellent copies can be prepared by electrophotographic means. Hitherto it has been recognised as advisable, when paper was used as support ,tfor the photoconductive layer, for special pretreated paper incapable of being penetrated by organic solvents to be used. The polymers of N-vinyl carbazoles can be applied in the form of solutions in organic solvents even to untreated base papers without excessive penetration of the coating solution taking place.

Although the nature of the polymers of the N-vinylcarbazoles makes the addition of other substances unnecessary, plasticizers and other resins, e.g. ketone resins, may if desired be added to photoconductive layers prepared in accordance with the invention, which in some circumstances could result in improvements, for example, in light sensitivity. Resins which are suitable to be added to the polymerized N-vinyl-carbazoles include also synthetic polymers or other organic colloids. As examples of such resins the following substances are stated:

(a) Natural and synthetic resins, e.g. balsam resins, phenol resins and other resins modified with colophony, coumarone resins and indene resins and the substances covered by the collective term synthetic lacquer resins, which includes processed natural substances such as cellulose ether, see the Kunststofftaschenbuch (Plastics Pocket Book) published by Saechtling-Zebrowski (11th edition, 1955, page 212 onwards);

(b) Polymers (including co-polymers) such as the polyvinyl chlorides, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohols, polyvinyl ethers, polyacrylic and polymethacrylic esters, and polystyrene and isobutylene polymers;

(c) Polycondensates, e.g. polyesters, such as phthalate resins, alkyd resins, maleic acid resins, colophony esters of mixed higher alcohols, phenol-formaldehyde resins,

. la particularly colophony-modified phenol-formaldehyde condensates, urea-formaldehyde resins, melamine-formaldehyde condensates, aldehyde resins, ketone resins of which particular mention is to be made of AW 2 resins of the firm Badische Anilin- .und Sodafabrik, zyleneformaldehyde resins and polyamides; and

(d) Poly-adducts, such as polyurethanes.

Other additives which may if desired be used, include pigments such as zinc oxide or titanium dioxide and also other photoconductive organic substances.

The polyvinyl carbazole foil, or support carrying a layer comprising polyvinyl carbazole, may be utilized for the production of images by electrophotographic means, for example, as follows:

When the photoconductive layer has been charged, by means of for example a corona discharge with a charging apparatus maintained at 6000 to 7000 volts, the thus sensitized layer is exposed to light under a master or by episcopic or diascopic projection and is then dusted over in known manner with a suitable developing agent such as a resin powder colored with carbon black. The image that now becomes visible can easily be wiped oif, and therefore needs to be fixed; it can for example, be heated briefly to approximately C. by means of an infrared radiator. The temperature need not be as high as this if the heat treatment is carried out in the presence of vapours of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol. The powdered image can also be fixed by means of steam. From positive masters, positive images of good contrast are produced.

After being fixed on a support these electrophotographic images can be converted into printing plates: the support, e.g. the paper or plastic foil, is wiped over with a solvent for the photoconductive layer, e.g. alcohol, or acetic acid and then rinsed with water and rubbed in with greasy ink in known manner. In this way positive printing plates are obtained which can be set up in an oflset machine and used for printing. They give very long runs.

If transparent supports are used the electrophotographic images can also be used as masters for the production of further copies on any sort of light sensitive sheets. In this respect the photoconductive compounds to be used as provided by the invention are superior to substances such as selenium or zinc oxide, inasmuch as the latter give cloudy layers.

The following examples are inserted for the purpose of illustrating the present invention, without any intention of limiting the scope thereof. The polyvinyl carbazoles disclosed in the examples are polymerization products of N-vinyl-carbazole.

Examples l) A solution of 10 gms. of polyvinyl carbazole in 150 ml. of benzene is applied to paper by means of a coating hopper and the coated paper is dried. The solution is applied onto the paper until the thickness of the dried layer amounts to 5 1.. A larger quantity of the solution can be applied in order to obtain a dried layer of an essentially uniform thickness of up to 20a.

The coated paper is negatively charged to about 300 volts by means of a corona discharge, exposed for a few seconds under a positive transparent master to the light of a high-pressure mercury vapour lamp watts, 30 cm. distance) and dusted over with a developer comprising a mixture of 100 gms. of glass balls (approx. a) and 2.5 gms. of a toner the particle size of which is 20-50;! Said toner can be prepared by fusion of:

as Perless Black Russ 552 produced by Druckfarbenfabriken Gebr. Hartmann, Concentra G.m.b.H., Frankfurt-Main 7 thereby made permanent (fixed). It has good contrast.

If a transparent paper is' used as support for the photo! electrically conductive layer, the images produced are suitable as copying masters (intermediate originals) for the production of duplicates by 'any convenient photo reproduction method, a 1

(2 6 grns. of polyvinyl carbazole and 0.3' gm. of the dyestuif Rhodamine B extra (see the foregoing table of dyestuffs) are together dissolved in 150 ml. of benzene and the solution is applied to paper as a coating and dried.

The coated paper can be positively charged by means of a corona discharge, the thus sensitized paper exposed under a positive transparent master to the light of a highpressure mercury vapour lamp for M second and dusted over with a developer consisting of methyl cellulose as carrier and the toner described in Example 1. A positive image of the master becomes visible which can be fixed by heating.

(3) 20 gms. of polyvinyl carbazole are dissolved in a mixture of 50 ml. of methylene chloride, 80 ml. of

From this solution a benzene and 20 ml. of dioxane. transparent foils are cast in known manner."

The foil produced can be charged by means of a corona 8 Paper is coated with this solution by means of a hopper device, and the coating dried; The coating in the paper can be negatively charged by means of acorona discharge and then an image of one side of a sheet printed on both sides can be projected episcopically on the charged paper to produce an electrostatic latent image of the said side. The electrostatic latent image is treated with a developer consisting of finely divided glass balls and a resin and carbon-black mixture, and fixed for example by heating.

(8) 10 gms. of a modified polyindene resin (such as that known as Gebaganharz I/SO sold by the firm Verkaufsvereinigung fiir Teererzeugnisse A.G., Essen) are dissolved in 135 gms. of ethylene glycol'monomethyl ether, andlO gms. of polyvinyl carbazole are then added to the solution thus obtained. A suspension is formed which is ground in a ball-mill down to a particle size of from 0.5 to I This suspension is applied by means of casting equipment onto paper advancing at a speed of 3.5 in. per minute. After drying the coated layer which contains 17 gms. per sq. m. of solid substance, the paper can be negatively charged by means of a corona discharge and can then be used for the production of direct images according to the procedure described in Example 1. Images which show a very good 7 contrast are obtained.

(9) 40 gms. of a water soluble amine resin (for example, the product sold by the firm Chemische Werke discharge to render it light-senstive, and exposed beneath a master for 15 seconds to the light of a high-pressure mercuryvapour lamp. The exposed foil with the latent electrostatic image of the master is powdered over with the developer described in Example 1 and the image that has been made visible is fixed by heating. (4) 10 gms. of polyvinyl carbazole and 0.02'0.1 gm. of the dyestuif Rhodamine B extra (see. the foregoing table of dyestuifs) are dissolved in a mixture of 75 ml. of trichloroethylene, 10 ml. of chloroform and 10 ml. of methylene chloride and the solution is cast into a thin,

transparent, red-coloured foil. The dyestutf present ren-' ders this foil, when charged, sensitive in the visible region of the spectrum.

The foil can be subjected to a corona discharge, exposed under a positive master for 4 second to the light of a high-pressure mercury vapour lamp and dusted over with a developer containing coloured resin particles, such as the developer described in Example 1. A positive image is obtained which can be fixed by heating.

(5) 16.5 gms. of polyvinyl carbazole and 0.033 gm. of the dyestuif Rose Bengal {see the foregoing table of dyestuffs) are together dissolved in 500 ml. of benzene and paper is coated with this solution. The coated paper is dried. The coating on the paper can be negatively charged by means of a corona discharge, and then exposed under a positive transparent master for about 0.5 second to the light of a 300-watt incandescent lamp;'the exposed side is then powdered over with developer such as that described in Example 1, when a positive image of the master is obtained, which can be fixed by heating.

6) Theprocedure described in Example 1 is followed except that the coating solution used contains 10 gms. of ketone resin (for example the resin known as Kunstharz AP produced by the Chemische Werke Hills A.G., Marl/Kr. Recklinghausen) as well as 10 gms. of polyvinyl carbazole, in 150 ml. of benzene. The coated paper is dried, then negatively charged by means of a corona discharge and exposed undera positive transparent master for three seconds to the light of a 125-watt high-pressure mercury vapour lamp at a distance of cm. An electrostatic positive image is obtained which is developed and fixed by steam treatment.

(7) 10 gms. of polyvinyl carbazole and'0.2 gm. of the dyestulf Ethyl Violet (see the foregoingtable of dyestuffs) are together dissolved in 200 ml. of benzene.

slightly heating it. The

Albert, Wiesbaden-Biebrich, under the registered trademark Resamin 403 F), are dissolvedin a mixture of 400 gms. of water and 30 gms. of bu-tanol. To the solution thus obtained, 1.2 gms; of ammonium thiocyanate and 40 gms. of polyvinyl-carbazole are added. The suspension thus obtained is most finely ground in a ballmill and is then applied onto paper by means of a coating device. After drying the applied layer, the paper is, heated for another 5 minutes at a temperature of C. The 'coated paper is used for the electrophotographic process described in Example 1. From a positive master positive images are obtained.

10) 0.7 cc. of a l-molar solution of dichloro-acetic acid in benzene is added to a solution of 9.6 gms. of polyvinyl carbazole in 135 gms. of benzene. The solution thus obtained is applied onto paper and is then dried. On this paper now provided with a polyvinyl carbazole layer, direct images may be produced electrophotographically as follows:

'of the apparatus being kept at 6000 to 7000 volts. The

electrostatically charged paper is exposed under a trans parent positive master to light for 1 second using a Watt high-pressure mercury yapour lamp at a distance of 30 cm. Subsequently the paper is dusted over with a resin powder, coloured with carbon black. The finely divided resin remains at those parts of the polyvinylcarbazole layer which have not been struck by light during exposure and thus a positive image of the original becomes visible, which is'then. made stable (fixed) by image shows a very good contrast.

(11) A solution in "90 gms. of methylene chloride of 6.4 gms. of polyvinyl carbazole and 0.6 cc. of a l-molar ZnCl -solution in tetrahydrofuran is applied onto an acetyl-cellulose foil or other transparent plastic foil or onto transparent paper. After evaporation of the solvent, a resulting polyvinyl carbazole layer adheres firmly to the surface of the foil. Electrophotographic images can be produced on the coated foil as described in Example 1. The'time of exposure to light under a positive master using a 125 watt mercury vapour lamp at a distance of 30 cm. amounts to 1 second. The images after developing or fixing maybe used as intermediate originals to produce prints using any light-sensitive material.

(12) 5 gms. of polyvinyl carbazole are dissolved in 90 gms. of benzene and to the solution 0.21 cc. of a 1- molar solution of p-toluene sulphonic acid in methanol is added. This solution is applied onto an aluminum foil the surface of which has been roughened by brushing. After evaporation of the solvent, a polyvinyl carbazole layer remains which adheres firmly to the surface of the foil. The production of a direct image of a positive original is efiected as described in Example 10. The time necessary for exposure to light amounts to 1 second. From the positive transparent original, a positive powder image is obtained, which is then fixed. The aluminum foil bearing the fixed image can be converted into a positive printing plate by treating the image-bearing side of the foil with toluene, rinsing it with water and applying greasy ink and a 1% phosphoric acid solution.

(13) 6.4 gms. of polyvinyl carbazole are dissolved in 90 gms. of benzene, and 326 cc. of a l-molar solution of sulphuric acid in tetrahydrofuran, and 6.5 gms. of the dyestufi Rhodamine B extra (see the foregoing table of dyestufis) in 1 cc. of methanol, are added thereto. The resulting solution is applied onto paper which is permeable to light and whose pH-value is about 5. Having been dried the coated paper is electrically charged negative by means of a corona discharge apparatus. The electrostatically charged paper is placed with its coated side contacting a book-page printed on both sides as original, and is exposed to light for 3 seconds by means of a 100-watt incandescent lamp. Exposure is thus effected through the copying paper. After exposure, the electrostatic latent image is dusted with a resin powder colored with carbon black, in known manner. A positive reversed image is obtained, which shows good contrast. By firmly pressing paper or a plastic foil onto the powder image obtained, the image can be transferred onto the paper or foil, and a non-reversed image of the book-page is thus obtained. During the transfer operation on the powder image, an electric field may, as is well-known in the art, be applied to the paper or foil, to which the reversed powder image is intended to be transferred. If the paper or foil (known as transfer material) is transparent, the copies produced thereon are suitable as intermediate originals for further copying such as printing onto diazotype paper or blue-print paper.

(14) 5 gms. of polyvinyl carbazole are dissolved in 100 gms. of toluene and the solution thus obtained is mixed with 0.21 cc. of a l-molar solution of ferric chloride in diethyl ether. This solution is applied onto paper which is then dried. For the production of an image, the coated paper is processed as described in Example 10. Using for the exposure under a master, a 125 watt high pressure mercury vapor lamp is used at a distance of 30 cm., the exposure time amounts to 0.5 second. From a positive master a positive image showing very good contrast is obtained.

(15) 7 gms. of polyvinyl carbazole are dissolved in 100 gms. of benzene and to the solution thus obtained there are added (a) 0.73 cc. of a l-molar solution of chloroacetic acid in methanol and (b) 7 gms. of the dyestufi acid violet 6 EN (see the foregoing table of dyestufis) in 1 cc. of methanol.

The mixture is applied onto paper which is then dried. The paper may be provided with a positive charge by means of a corona-discharge apparatus rendering it sensitive to light-rays, exposed for 1 second under a positive transparent original to light from a 40 watt incandescent lamp at a distance of 30 cm. and then dusted over with a resin powder coloured with carbon black. A positive image of the original is thus made visible and is fixed by heating.

(16) 0.9 cc. of a l-molar solution of boron tritluoride (in the form of boron trifiuoride etherate) in benzene and a solution of 4 m-gms. of the dyestufi Rhodamine B extra (see the foregoing table of dyestuffs) in 2 gms. of

10 r methanol, are added to a solution of 9.6 gms. of polyvinyl carbazole in gms. of benzene. The solution thus obtained whose kinetic viscosity is about 5 centistokes, is applied as a layer onto paper, and dried. The paper may then be provided with a negative electric charge by means of a corona discharge apparatus, and the charged paper exposed to form an electrostatic latent image, for example by episcopic projection of a bookpage. With a light intensity (candle power) of the light source of 30 Lux., an exposure time, of 1 second is necessary. In order to make the image visible, the layer side of the exposed paper is treated with a developer consisting of a mixture of small glass beads and very finely divided particles of a resin-carbon-black mixture. The black colored resin which becomes positively charged triboelectrically sticks to those parts of the polyvinyl canbazole layer which have not been struck by light during exposure, and a positive image is thus obtained, which is fixed by slightly heating it. The image shows good contrast.

(17) The procedure described in Example 10 is followed except that for coating the paper, a solution is used, prepared by mixing gms. of benzene containing 9.6 gms. of polyvinyl carbazole dissolved therein, 07 cc. of a l-molar solution of dichloroacetic acid in benzene and 2 mgms. of the dyestutf Victoria blue B (see the foregoing table of dyestuffs) in 1 cc. of methanol. When using a 40 watt incandescent lamp at a distance of 30 cc. the exposure time needed is 1 second. An image may be pro duced also from a book-page, both sides of which have been printed, by episcopic projection. The images show the half-tones and the full-tones with good contrast.

(18) 9.6 gms. of polyvinyl carbazole and 0.111 g. of 2-methylanthraquinone are dissolved in cc. of benzene, the solution thus obtained is applied onto paper and dried. On the paper thus coated with a polyvinyl carbazole layer, a direct image can be electrophotographioally produced by providing the layer with a negative electric charge by means of a corona discharge apparatus, exposing the charged layer of one second under a positive transparent original to light from a high-pressure mercury vapor lamp of 125 watts at a distance of 25 cms., and subsequently dusting (developing) the exposed layer with a resin powder colored with carbon black in a manner known per se. A positive image of the transparent original becomes visible, which is made stable (fixed) by slightly heating it. The image shows good contrast.

Instead of 2-methylanthraquinone, other quinones can be added in equivalent quantity to the polyvinyl carbazole solution, for example, another substitution product of anthraquinone, anthraquinone itself, benzoquinone, naphthoquinone, or a substitution product of the two last mentioned quinones. By using a transparent support such as a sheet of cellulose acetate instead of paper, the positive copy produced electrophotographically can be used as a master for printing on to other light sensitive layers.

19) 1.2 cc. of a l-molar solution of dichloroacetic acid in toluene, 0.08 gm. of Rhodamine B extra (see the foregoing table of dyestuffs) dissolved in 8 cc. of methanol, and 0.8 gm. of anthraquinone, are added to 400 cc. of a 20% solution of polyvinyl carbazole in toluene. The solution thus obtained is applied onto paper to form thereon a polyvinyl carbazole layer. After drying the coated layer the paper is negatively charged by means of a corona discharge and a latent image is produced on this paper from a bookpage by episcopic projection. The

' paper is then treated on its layer supporting side by means of a developer, consisting of little glass beads and a very finely divided resin-soot-mixture. The black colored resin remains adhering to the areas not struck by light during the exposure, and a positive image becomes visible which is made stable (fixed) by gently heating it. The image shows good contrast effects.

(20) 16 gms. of polyvinyl canbazole and 0.21 gm. of pyrene-B-aldehyde are dissolved in 220 cc. of toluene,

and the solution is applied onto an aluminum foil. After.

evaporation of the solvent a layer remains adhering firmly to the surface of. the foil. With the coated aluminum. foil images can be produced from patterns by the electrophotographic process in a manner known.per se, from which images copies with good contrast can be obtained 7 on paper by transference.

, The time of exposure under the. same conditions as described in Example 18 amounts to 2 seconds.

(21) 21.4 gms. of polyvinyl carbazole and 0.25 gm. of benzil are dissolved in 280 cc. of benzene and then 0.05 g. of the dyestufl Victoria blue B (see the foregoing-table of dyestuffs) in cc. of methanol is added to this solution,

which is subsequently applied onto non-transparent opaque paper which is permeable to light (translucent) and dried. The polyvinyl carbazole layer thus provided on the paper, is negatively charged by means of a corona discharge apparatus and is put with its layer-side upon a doublesided printed book-page which serves as an original lying on a backing of black paper. It is then exposed to light under a 100 watt incandescent bulb for 2 seconds. The exposure takes place reflex-wise from the back side of the coated paper through the paper sheet.

After exposure the electrostatic latent image'on the paper is powdered with resin-soot-powder and a positive reversed image, rich in contrast, is obtained which image is transferred to a transfer sheet of paper or plastic foil, which is firmly pressed on the powder image A nonreversed copy of the book-page used as pattern is obtained. The transference may also becarried out in the manner known per se wherein an electric field is applied to'the transfer material. The transferred image is then fixed. If the paper or the plastic foil (transfer sheet) are transparent the non-reversed image obtained can be used as an intermediate original for making further copies for example on diazotype or blueprint paper. e

(22) The procedure described in Example 18 is followed, except that for coating the paper a solution of 44 gms. of polyvinyl carbazole and 0.42 gm. of indandione- 1,3 (l,3diketohydrindene) in 820 cc. of benzene, is used. With the material produced positive images also rich in contrast are obtained. The exposure of the charged material s elfected under a 125'watt high-pressure mercury vapor lamp at a distance of about 25 cms., with an exposure time of 2 seconds.

(23) 6.5 gms. of polyvinyl carbazole and 0.05 gm.-of acen-aphthenequinone-dichloride are dissolved in 120 cc. of benzene. The resulting solution is applied onto paper and dried. By further processing the coated paper for the purpose of producing images by Way of the electrophotographic method as described in Example 18 a positive image is obtained which can be fixed by treating it with trichloroethylene vapor. Time of exposure 2 seconds.

(24) The procedure described in Example 18 is followed, except that for coating the paper a solution is used of 50 cc. of benzene containing 4 gms. of polyvinyl carbazole and 0.065 g. of phthalic anhydride. The time of exposure necessary for producing positive latent elect-rostatic images amounts to 1 second. t Y

(25) 100 gms. of polyvinyl carbazole, 15 gms. of l-chloroanthraquinone and 1 gm. of the dyestutf Acid Violet 6 EN (see the foregoing table of dyestuffs) are dissolved in 1700 cc. of benzene. The resulting solution .is applied onto paper and dried. After the paperhas been electrically positively charged bymeans of a corona discharge apparatus it is exposed for 1.5 seconds under a positive original to light from a 100 watt incandescent bulb at a distance of about 20 cuts, and is subsequently developed by means of a developer consisting of granular methylcellulose and finely divided resin-soot-powder. The powder image can be fixed by heating. a

(26) The'procedure described in Example 9 is followed except that for coating the paper a mixture issued prepared by mixing a solution of 10 gms. of polyvinyl car- 'oazole and 0.126 gm. of l-chloro-anthraquinone in 200 cc. of benzene, a solution of 0.06 g. of .maleic acid in 30 cc. of tetrahydrofurane, and a solution of 0.05 g. of the dyestuff Rhodamine B extra (see the foregoing table of dyestuffs) in 5 cc. of methanol. The paper is exposed for 5 seconds under a 40 watt incandescent lamp at a distance of 25 cms. After developing and fixing the images produced show good contrast.

Modifications within the scope of the invention may be made in the procedures specifically. described above, as will be apparent to those skilled in the art. In particular, the types of exposure methods prescribed (e.g., contactprinting, and episcopic projection for copying from opaque or double-sided masters) may be interchanged at will.

What we claim is:

l. A photographic reproduction process which comprises exposing an electrostatically charged photoconductive insulating layer comprising solid polyvinylcarbazole to a light image, whereby the light-struck area is discharged, and developing the resulting image with an electroscopic material.

2. A process according to claim 1 in which the photoconductive layer also contains a dyestuif sensitizer.

3, A process according to claim 1 in which the photoconductive layer also contains a compound selected from the group consisting of mineral acids, metal halides, boron halides and compounds containing a carbonyl group.

4. A process according to claim 1 in which the photoconduct-ive layer also contains a mineral acid.

5. A process according to claim 1 in which the photoconductive layer also contains a carboxylic acid.

6. A process according to claim 1 in which the photo conductive layer also contains an acid anhydride.

7. A process according to claim 1 in which the photoconductive layer also contains a metal halide.

8. A process according to claim 1 in which the photoconductive layer also contains a. boron halide.

9. A process according to claim 1 in which the photoconductive layer also contains a compound containing a carbonyl group.

10. A process according to claim 1 in which the photoconductive layer also contains a dyestufl? and a compound selected from the group consisting of mineral acids, metal halides, boron halides, and compounds containing a carbonyl group.

11. A process according to claim 1 in which the photoconductive insulating layer also contains a different resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,072,465 Reppe et al. 'Mar. 2, 1937 2,297,691 Carlson Oct. 6, 1942 2,663,636 Middleton Dec. 22, 1953 2,697,028 Baker et al. Dec. 14, 1954 2,800,559 Ubbelohde July 23, 1957 OTHER REFERENCES a. .L a... 

1. A PHOTOGRAPHIC REPRODUCTION PROCESS WHICH COMPRISES EXPOSING AN ELECTROSTATICALLY CHARGED PHOTOCONDUCTIVE INSULATING LAYER COMPRISING SOLID POLYVINYLCARBAZOLE TO A LIGHT IMAGE, WHEREBY THE LIGHT-STRUCT AREA IS DISCHARGED, AND DEVELOPING THE RESULTING IMAGE WITH AN ELESTROSCOPIC MATERIAL. 